Fresh-keeping method for prolonging normal-temperature shelf life of broccoli based on electron beam irradiation technology

Abstract

The invention discloses a preservation method for prolonging the shelf life of broccoli based on an electron beam irradiation technology, which comprises the following steps: firstly, preparing a green-protecting solution consisting of sodium copper chlorophyllin (0.25-0.35 g / L), ascorbic acid (0.90-1.05 g / L) and tea polyphenol (1.70-1.80 g / L), and adjusting the pH value to 6.0-6.5; soaking the pretreated broccoli in a green-protecting solution according to a material-liquid ratio of (1: 3)-(1: 5) g / mL, carrying out 550-650W microwave treatment for 0.5-1min, and standing for 15-25min; blanching with hot water at 95-105 DEG C for enzyme deactivation for 25-35 s, and cooling with ice water to room temperature; and finally, performing vacuum packaging, and performing 0-8 kilogray electron beam irradiation. According to the method, the broccoli is pretreated and combined with an irradiation sterilization technology, so that the fresh-keeping period of the broccoli is remarkably prolonged, and the method is suitable for large-scale processing and storage scenes.

Description

Technical Field

[0001] This invention relates to the field of broccoli preservation technology. Specifically, it describes a method for extending the shelf life of broccoli based on electron beam irradiation technology. Background Technology

[0002] Broccoli is a widely consumed cruciferous vegetable with high nutritional value, rich in functional components such as sulforaphane, and possessing health potential including anti-cancer properties. However, broccoli is highly susceptible to spoilage after harvesting (it quickly turns yellow, loses firmness, and suffers nutrient loss during storage), and fresh broccoli has a very short shelf life (2-3 days at room temperature, and a maximum of 3-4 weeks refrigerated). Various methods have been employed to slow down the quality decline of broccoli during storage, commonly including chemical methods (solution soaking) and controlled atmosphere storage. However, these methods cannot effectively eliminate microbial growth and may leave chemical residues (harmful to humans) and are costly.

[0003] Electron beam irradiation is a non-thermal, environmentally friendly technology that uses high-energy electron beams to directly destroy the DNA of microorganisms or indirectly destroy them by generating active free radicals, causing them to die or lose their reproductive ability. It has the characteristics of being environmentally friendly, highly efficient and rapid sterilization, leaving no chemical residues, maintaining the sensory and nutritional quality of food, low energy consumption, and relatively simple operation. It has become a hot topic in fruit and vegetable preservation research and has been widely used in the preservation of fruits and vegetables, showing significant effects.

[0004] However, despite the significant advantages of electron beam irradiation technology in preservation, its application as a standalone treatment for broccoli still has certain limitations. While high doses of electron beam irradiation effectively sterilize, they can also negatively impact the texture of fruits and vegetables. In particular, when using high doses of electron beam irradiation alone, although it can effectively kill microorganisms, the different maximum doses that different fruits and vegetables can tolerate may lead to poorer preservation results, thus limiting the practical application of electron beam irradiation in preservation. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to provide a method for extending the shelf life of broccoli based on electron beam irradiation technology, so as to solve the technical problem that the sterilization effect of broccoli preservation in the prior art is not significant.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0007] A method for extending the shelf life of broccoli based on electron beam irradiation technology includes the following steps:

[0008] Step 1: Prepare the green protection solution and adjust the pH of the solution to 6.0-6.50, then set aside.

[0009] Step 2: Soak the selected broccoli in a greening solution and then microwave it.

[0010] Step 3: After microwave treatment, the broccoli is subjected to high-temperature enzyme inactivation treatment, and then immediately placed in ice water to cool rapidly to room temperature;

[0011] Step 4: Seal the treated broccoli in a vacuum-sealed bag and then subject it to electron beam irradiation.

[0012] This invention constructs a multi-step preservation system by synergistically treating broccoli with a specific pH-controlled greening solution, microwave-assisted penetration, high-temperature enzyme inactivation, and electron beam irradiation. Components in the greening solution rapidly penetrate the broccoli tissue under microwave action, delaying chlorophyll degradation and enhancing antioxidant capacity. High-temperature enzyme inactivation effectively inhibits enzyme activity, preventing browning, and combined with ice-water cooling, locks in the tissue morphology. Electron beam irradiation, applied on this basis, fully utilizes its highly effective bactericidal effect while maintaining a good appearance, inhibiting microbial growth and secondary contamination. Simultaneously, the antioxidant components in the pretreatment greening solution mitigate potential oxidative damage caused by irradiation. The interdependent and synergistic effects of each treatment step significantly delay broccoli yellowing, decreased firmness, and MDA accumulation, maintaining its sensory quality and nutritional value, thus effectively extending shelf life under normal temperature conditions.

[0013] The above-mentioned method for extending the shelf life of broccoli based on electron beam irradiation technology includes, in step one, a chlorophyll-protecting solution comprising the following components at concentrations: sodium copper chlorophyll salt 0.25-0.35 g / L, ascorbic acid 0.90-1.05 g / L, and tea polyphenols 1.70-1.80 g / L. Soaking the broccoli in the chlorophyll-protecting solution slows down chlorophyll degradation and extends its shelf life.

[0014] In the above-mentioned method for extending the shelf life of broccoli based on electron beam irradiation technology, in step one, the greening solution includes the following components at the following concentrations: sodium copper chlorophyllin 0.30 g / L, ascorbic acid 1.00 g / L, and tea polyphenols 1.75 g / L.

[0015] In the above-mentioned preservation method for extending the shelf life of broccoli based on electron beam irradiation technology, in step one, the pH of the solution is adjusted to 6.5 by adding a regulator. At this pH, the greening solution is more stable, reducing the damage of the solution to the broccoli cells.

[0016] In the above-mentioned preservation method for extending the shelf life of broccoli based on electron beam irradiation technology, in step two, the ratio (m / V) of broccoli to the greening solution is 1:3-1:5 g / mL.

[0017] The above-mentioned preservation method for extending the shelf life of broccoli based on electron beam irradiation technology has a material-to-liquid ratio (m / V) of broccoli to the greening solution of 1:4 g / mL.

[0018] In the above-mentioned method for extending the shelf life of broccoli based on electron beam irradiation technology, the regulator is an alkaline solution, which can be a sodium carbonate solution.

[0019] In the above-mentioned preservation method for extending the shelf life of broccoli based on electron beam irradiation technology, the specific method of microwave treatment in step two is as follows: The broccoli soaked in the greening solution is treated in a microwave device with a power of 550-650 W for 0.5-1 min, and then left to stand for 15-25 min. This promotes faster penetration of the greening solution into the broccoli tissue, improving the effectiveness of the greening solution.

[0020] In the above-mentioned preservation method for extending the shelf life of broccoli based on electron beam irradiation technology, in step two, the selected broccoli is pretreated before being soaked in the greening solution. The pretreatment method is as follows: the selected broccoli is washed sequentially with sodium hypochlorite solution and water, wherein the concentration of sodium hypochlorite in the sodium hypochlorite solution is 0.4%.

[0021] The above-mentioned method for extending the shelf life of broccoli based on electron beam irradiation technology includes a blanching process in step three, where the blanching temperature is 95-105 ℃ and the blanching time is 25-35 s. The deterioration of broccoli during storage is mainly caused by the action of chlorophyll-degrading enzymes and peroxidases. Blanching effectively destroys these enzymes, maintaining the good color and quality of the broccoli during storage.

[0022] In the above-mentioned method for extending the shelf life of broccoli based on electron beam irradiation technology, the radiation dose of electron beam irradiation in step four is 0-8 kGy.

[0023] In the above-mentioned method for extending the shelf life of broccoli based on electron beam irradiation technology, the radiation dose of electron beam irradiation in step four is 6 kGy.

[0024] The technical solution of the present invention achieves the following beneficial technical effects:

[0025] This invention achieves a significant extension of the shelf life of broccoli through a multi-step synergistic treatment process, including pretreatment (soaking in a green-protecting solution at a specific pH + microwave-assisted permeation + hot water blanching to inactivate enzymes) and electron beam irradiation. Specifically, this is reflected in the following aspects:

[0026] (1) This invention soaks broccoli in a greening solution composed of sodium copper chlorophyll, ascorbic acid and tea polyphenols, adjusts its pH, and combines microwave-assisted penetration to promote the uniform distribution of the greening agent, so that the components in the greening agent solution can quickly penetrate into the broccoli tissue, delay chlorophyll degradation, extend the shelf life, and reduce its color difference value; and the components in the greening solution are relatively natural, resulting in less chemical residue and lower cost.

[0027] (2) The present invention effectively inhibits the activity of enzymes such as chlorophyll-degrading enzymes and peroxidases by high-temperature short-time blanching, avoiding the inability of electron beam irradiation to effectively inhibit enzyme activity, preventing broccoli browning, maintaining the good color and quality of broccoli during storage, and the rapid cooling with ice water quickly terminates the heat reaction, preventing the residual heat of blanching from excessively softening the broccoli tissue, and locking in the tissue shape and color.

[0028] (3) Pretreatment has reduced the initial microbial load and enzyme activity to a certain extent and enhanced the antioxidant capacity of the tissue. When electron beam irradiation is applied at this time, especially at an optimized dose of 6 kGy, it can fully exert its bactericidal function in the stable internal environment created by pretreatment without significantly affecting its appearance, inhibiting secondary pollution and quality deterioration during storage. The antioxidant components in pretreatment (such as tea polyphenols and ascorbic acid) can also alleviate the oxidative damage that may be caused by irradiation, forming a complementary effect.

[0029] In summary, the various processing steps of this invention are interdependent and work synergistically to construct a multi-layered preservation system, which can effectively delay the degradation and yellowing of chlorophyll in broccoli, inhibit the decrease in firmness and the accumulation of MDA to a certain extent, maintain good sensory acceptance and nutritional value, and enable broccoli to achieve a better preservation effect to meet market demand. Attached Figure Description

[0030] Figure 1 Comparison of the appearance changes of broccoli after electron beam irradiation treatment;

[0031] Figure 2 (a) Comparison of a* values ​​of broccoli under different radiation doses; Figure 2 (b) is a comparison chart of b* values ​​of broccoli under different radiation agents; Figure 2 (c) Comparison of L* values ​​of broccoli under different radiation doses; Figure 2 (d) is a comparison of the color difference of broccoli under different radiation doses;

[0032] Figure 3 A comparison chart of broccoli firmness under different radiation doses;

[0033] Figure 4(a), 4(b), 4(c), and 4(d) are radar charts showing the quantitative scores of 20 food professionals on hardness, odor, color, and overall acceptability from left to right and from top to bottom on days 0, 2, 4, and 6, respectively.

[0034] Figure 5 (a), 5(b), and 5(c) are comparison graphs of the effects of different radiation doses on the chlorophyll content, total phenols, and DPPH free radical scavenging rate of broccoli.

[0035] Figure 6 Heat maps of flavor compounds for the CK group, 0kGy group and 6kGy group;

[0036] Figure 7 Heatmap of flavor compounds with VIP value > 1;

[0037] Figure 8 This is a graph showing the changes in the amount of flavor compounds in broccoli. Detailed Implementation

[0038] Fresh broccoli is popular among fitness enthusiasts and those trying to lose weight due to its high dietary fiber content and abundance of anti-cancer substances. However, because broccoli undergoes vigorous respiration and metabolism after harvesting, it is prone to yellowing, dehydration, aging, and rotting, making it difficult to preserve.

[0039] 1. Preservation methods to extend the shelf life of broccoli

[0040] In this embodiment, the broccoli was purchased from an agricultural product market in Beijing. Broccoli with intact shape and appropriate size were selected, and old leaves, rotten leaves, and weeds were removed. After purchase, the broccoli was immediately transported to the laboratory under refrigeration at 4 ℃, and samples with similar maturity, size, and color and no mechanical damage were selected for preservation experiments.

[0041] The selected broccoli was repeatedly washed with water and sodium hypochlorite (one rinse with clean water + 5 minutes with sodium hypochlorite + 3 rinses with distilled water) to remove impurities such as sand, gravel, and insect eggs from the leaves.

[0042] Prepare a chlorophyll-protecting solution comprising 0.30 g / L sodium copper chlorophyll, 1.00 g / L ascorbic acid, and 1.75 g / L tea polyphenols. Adjust the pH of the solution to 6.50 using sodium carbonate. Immerse the raw materials in the prepared chlorophyll-protecting solution (material-to-liquid ratio 1:4), treat with a 600 W microwave oven for 1 min, and then let stand for 20 min.

[0043] The microwaved broccoli was then blanched to inactivate enzymes (100 ℃, 30 s), and then immediately placed in ice water at 0 ℃ to cool rapidly to room temperature.

[0044] The treated broccoli was sealed in 50 g bags in polyethylene vacuum packaging bags and then subjected to electron beam irradiation treatment with a radiation dose of 0-8 kGy. In this study, the radiation dose gradient of electron beam irradiation was set to 0, 2, 4, 6, and 8 kGy. A control group (CK) was also set up (the baseline state without any preservation intervention; the broccoli in this group was directly stored after washing).

[0045] After electron beam irradiation treatment, the broccoli was stored for 6 days at a constant temperature of 25 ℃, relative humidity of 95%-100%, oxygen concentration of about 2%, and carbon dioxide concentration of about 10%. The quality changes were assessed by visual inspection and photographed daily. Some broccoli were frozen in liquid nitrogen and then stored at -20 ℃ until the measurement was performed.

[0046] 2. Broccoli Evaluation Methods

[0047] 2.1 Measurement of Apparent Indicators

[0048] 2.1.1 Hardness Measurement

[0049] A TA10 cylindrical probe was used. Experiment type: full texture test; Test type: compression; Target mode: displacement; Pre-test velocity: 3.00 mm·s. -1 Test speed: 1.00 mm·s -1 Post-test speed: 3.00 mm·s -1 Trigger type: force; Trigger value: 5.00 g; Target value: 5.00 mm; Time: 5.00 s.

[0050] 2.1.2 Color Measurement

[0051] Color was measured using a portable colorimeter, and the results are expressed as L*, a*, and b* values. L* represents the light spectrum from 0 (black) to 100 (white), a* represents the green-red spectrum (+a*=red, –a*=green), and b* represents the blue-yellow spectrum (+b*=yellow, –b*=blue).

[0052] Using fresh broccoli from group CK on day 0 as the standard, the formula for total color difference (ΔE) is:

[0053]

[0054] 2.1.3 Sensory evaluation

[0055] A sensory evaluation panel of 20 food professionals was organized to conduct a sensory evaluation of the broccoli. Four attributes were used to quantitatively describe the broccoli, including firmness, odor, color, and overall acceptability, with quantitative scores ranging from 0 to 20.

[0056] 2.2 Determination of total bacterial count in broccoli

[0057] The determination of total bacterial count should refer to GB / T4789.2-2022 for the determination of total bacterial and fungal counts.

[0058] 2.3 Determination of chlorophyll, MDA content, total phenols, and DPPH scavenging rate in broccoli

[0059] 2.3.1 Chlorophyll content of broccoli

[0060] The total chlorophyll content was calculated using a formula obtained from the Nanjing Jiancheng chlorophyll content test kit.

[0061] Calculation formula: Total chlorophyll (mg / 100 g) = 100 × [20.2 × A645 + 8.02 × A663].

[0062] 2.3.2 Broccoli MDA content

[0063] The content of MDA was tested using the Nanjing Jiancheng MDA content test kit.

[0064] 2.3.3 Determination of total phenol content

[0065] Pre-freeze the broccoli in a -80 ℃ freezer, then freeze-dry, grind, and sieve. Accurately weigh 1.00 g of freeze-dried broccoli powder into a 50 mL centrifuge tube, add 20 mL of 80% methanol, and extract by sonication (40 ℃, 100 W, 30 min). Centrifuge (3500 rpm / min, 10 min) and collect the supernatant. Repeat the operation once and combine the supernatants.

[0066] The soluble polyphenol content was determined using the Folin-Ciocalteu method: 125 μL of sample solution or standard solution was mixed with 125 μL of Folin-Ciocalteu reagent and 0.5 mL of ultrapure water and reacted for 6 min. Then, 1.25 mL of 7% (m / V) Na₂CO₃ solution and 1 mL of distilled water were added and mixed well to start the reaction. After reacting for 2 hours in the dark at room temperature, the absorbance at 765 nm was measured using a microplate reader. Simultaneously, 125 μL of methanol was used as a blank control instead of the extraction solution, and gallic acid standards with different solubility gradients were prepared to construct a standard curve.

[0067] Accurately weigh 0.02 g of gallic acid, dissolve it in methanol, and dilute to 100 mL. Establish a standard curve using gallic acid as a standard, with values ​​of 0.04, 0.08, 0.12, 0.16, and 0.20 mg / mL. Total phenolic content is expressed as gallic acid equivalents per 100 g of dry broccoli, abbreviated as µg GAE / 100 g. The determination is repeated three times.

[0068] 2.4 Analysis of volatile flavor compounds in broccoli

[0069] Analysis of volatile compounds was performed using the method described below. The simplified procedure is as follows: Accurately weigh 4.0 g of fresh broccoli and transfer it to a 20 mL sealed headspace vial. Add 6 μL of 2-methyl-3-heptanone (as an internal standard) to the vial beforehand. After equilibration for 20 minutes, extract using a 50 / 30 μm divinylbenzene / carbon molecular sieve / polydimethylsiloxane (DVB / CAR / PDMS) fiber at 50 °C for 30 minutes. Subsequently, remove the fiber from the headspace vial and insert it into the injection port of a gas chromatography-mass spectrometry (GC-MS) system, and inject the sample at 230 °C. Separation was performed on a DB-WAX capillary column (60 m × 0.25 mm × 0.25 μm) using helium as the carrier gas at a constant flow rate of 1.4 mL / min. The GC column oven temperature program was set as follows: initial temperature 40°C, held for 3 minutes; then increased to 120°C at a rate of 4°C per minute; followed by an increase to 230°C at a rate of 10°C per minute, and held at this temperature for 5 minutes. The ion source temperature was maintained at 200°C, using full scan mode with a mass-to-charge ratio (m / z) increment of 1, covering a mass range of 40–400 m / z. Volatile compounds were qualitatively identified by matching the obtained mass spectra with those in the NIST 20 mass library. Using 2-methyl-3-heptanone as an internal standard, the relative abundance of each identified volatile compound was quantitatively analyzed by comparing the peak areas of each component with the internal standard.

[0070] 2.5 Statistical Analysis

[0071] All measurements were repeated at least three times, and results are expressed as mean ± standard deviation (SD). Statistical significance of the data was calculated using SPSS v.18.0 software via one-way ANOVA combined with Duncan's multiple range test. A p-value < 0.05 was considered statistically significant. Plotting was performed using Origin 2024 software.

[0072] 3. Results and Discussion

[0073] 3.1 Effects of electron beam irradiation on the appearance of broccoli

[0074] As storage time increased, the appearance of broccoli treated with different doses of irradiation showed significant differences. Figure 1The appearance changes of broccoli treated with different irradiation doses during storage were observed. The CK, 0 kGy, and 2 kGy groups began to yellow from day 2, while the 4 kGy group showed yellowing from day 4. Severe yellowing was observed in all these groups by day 6 of storage. It was also noted that the yellowing rate of the 0 kGy group was lower than that of the CK group, indicating that the pre-treatment for maintaining green color had a certain inhibitory effect on the deterioration of broccoli's color. The high-dose groups (6 kGy and 8 kGy groups) did not show severe yellowing until day 6, demonstrating that pre-treatment for maintaining green color combined with electron beam irradiation can effectively maintain the good appearance of broccoli during storage.

[0075] 3.1.1 Effect of electron beam irradiation on the color of broccoli

[0076] a*, b*, and L* are used to measure the color change of broccoli during storage. The a* value represents the red and green hue of the broccoli head; a higher value indicates a more reddish head. The b* value represents the yellow-blue hue of the head; a higher value indicates a more yellowish head. The L* value represents the brightness of the head; a higher value indicates a whiter head. The a*, b*, L* values, and total color difference of broccoli were measured from 0 to 6 days.

[0077] from Figure 2 As shown in (a), the a* value of broccoli under different treatment conditions gradually increased during storage. On day 0, the a* value of broccoli in the high-dose groups (6 kGy and 8 kGy) was significantly higher than that in the control group (CK), while there was no significant difference between the other treatment groups and the CK. This indicates that high-dose electron beam irradiation increases the a* value of broccoli, thus weakening its green phenotype. However, during subsequent storage, the rate of decrease in a* value for irradiation treatments at 4 kGy, 6 kGy, and 8 kGy doses was much lower than that in the CK group. These results suggest that although higher doses of electron beam irradiation initially increase the a* value of broccoli, they effectively delay the increase in a* value during storage, maintaining the green phenotype of broccoli. Figure 2 As shown in (b), the b* values ​​of broccoli treated with CK and 0 kGy and 2 kGy gradually increased during storage, while the b* values ​​of broccoli irradiated with 6 kGy showed no significant difference at days 2, 4, and 6, indicating that electron beam irradiation can slow down the increase in b* values ​​of broccoli during storage. Furthermore, the b* values ​​of the CK group were significantly higher than those of other groups at days 4-6, which may be due to the faster deterioration and yellowing of broccoli during these days of storage. Figure 2As shown in (c), there was no significant difference in L* values ​​under different doses of irradiation treatment. However, the L* value of the 6 kGy irradiation treatment was significantly higher than that of other groups during the storage period of 0, 2, 4, and 6 days. The L* values ​​of the 4 kGy and 8 kGy doses were lower than those of the CK group. Only the 6 kGy irradiation treatment improved the brightness of the broccoli. Figure 2 (d) It can be seen that electron beam irradiation can significantly reduce the total color difference of broccoli during storage. The color retention effect of the high-dose group is better than that of the low-dose group. Among them, the total color difference of 6 kGy and 8 kGy groups is greater than that of the CK group on day 0, but the total color difference on days 2, 4, and 6 is smaller than that of the CK group and the 0 kGy group. The maximum difference is reached on day 2, with the CK group (15.123) being 2.08 times greater than that of the 6 kGy group (7.273). In conclusion, electron beam irradiation after greening pretreatment can effectively delay the color change of broccoli, extend the storage period, and is dose-dependent.

[0078] 3.1.2 Effect of electron beam irradiation on the firmness of broccoli

[0079] Firmness is an important indicator of the texture and firmness of vegetables. Figure 3 It can be seen that electron beam irradiation treatment can significantly reduce the firmness of broccoli, and the degree of effect of different doses of electron beam irradiation treatment on the reduction of broccoli firmness varies. The firmness of all treatment groups in the figure can be divided into high-firmness and low-firmness groups. The experimental results show that there may be a "dose threshold" for the effect of electron beam irradiation on the firmness reduction of plants or their fruits: when the irradiation dose is ≥ the "dose threshold", electron beam irradiation may damage the plant cell wall structure, thus leading to a decrease in firmness. This is because the main components of plant cell walls are pectin, cellulose, and hemicellulose, which maintain the internal structure of plant fruits. Electron beam irradiation produces free radicals in plant fruits, which attack pectin and hemicellulose in the cells, damaging the cell wall structure. Low-intensity irradiation produces fewer free radicals, resulting in a weaker attack on enzymes; therefore, broccoli irradiated with low intensity can still maintain good firmness. High-intensity irradiation, however, cannot maintain high firmness in broccoli. The effects of pretreatment and different doses of electron beam irradiation on the firmness of broccoli during storage are shown in [Figure 1]. Figure 3 The results showed that the pretreatment alone reduced the firmness of broccoli, which may be due to the blanching process, as the high temperature damaged the cell wall structure of the broccoli. However, compared with the control group, the firmness of broccoli after pretreatment and irradiation at doses of 4, 6, and 8 kGy decreased by 65.16%, 67.35%, and 71.21% on day 0, respectively. The decreasing trend of broccoli firmness after high-dose electron beam irradiation combined with pretreatment has slowed down to some extent, indicating that broccoli irradiated by electron beam has a better ability to maintain its texture.

[0080] 3.1.3 Sensory evaluation

[0081] A sensory evaluation team of 20 food professionals conducted a sensory evaluation of the broccoli immediately after irradiation treatment. The sensory quality changes of the broccoli throughout storage were as follows: Figure 4 As shown in the figure, on day 0, both the single greening treatment and the combined greening and electron beam irradiation treatment reduced the sensory indicators of broccoli (including color, texture, and flavor). However, during storage (days 2-6), the overall acceptability of the irradiated group was consistently higher than that of the control group (CK). The 6 kGy group maintained the highest overall acceptability score (12.125) at the end of storage, a 76% improvement over the CK group (6.875). This indicates that electron beam irradiation after greening treatment effectively improved the overall acceptability of broccoli during storage. The CK group exhibited a more pronounced putrid odor during storage, severely impacting sensory evaluation results. This observation is consistent with other studies that found that electron beam irradiation at doses of 4 kGy and 6 kGy reduced undesirable sensory properties such as pungent odors and sulfurous off-odors in broccoli bud juice. This phenomenon is attributed to the fact that electron beam irradiation decomposes compounds that produce pungent and sulfurous off-odors, thus helping to maintain the overall flavor characteristics of broccoli bud juice during storage.

[0082] As a key freshness indicator, the CK group had the highest color score among all groups. The color scores of the groups treated with color protection pretreatment and irradiation all decreased to varying degrees, but the decrease in color score during subsequent storage was significantly less than that of the CK group. This is because the broccoli that did not undergo color protection and electron beam irradiation treatment yellowed the fastest, directly leading to its lower sensory score. Irradiated broccoli, on the other hand, effectively maintained its green color, delayed color deterioration, and maintained a better appearance. Figure 4 The results show that although the greening treatment significantly reduced the overall acceptability of broccoli in the early stages, the scores of the irradiated group remained high during storage after electron beam irradiation. This indicates that the combined effect of the greening pretreatment and electron beam irradiation is not by improving the quality of broccoli, but by effectively slowing down the rate of quality deterioration, thus maintaining the commercial value of broccoli.

[0083] 3.2 Effects of electron beam irradiation on chlorophyll and antioxidant capacity of broccoli

[0084] 3.2.1 Effect of electron beam irradiation on chlorophyll content in broccoli foliage

[0085] Chlorophyll, as a key green pigment in photosynthesis in higher plants, is the main material basis for maintaining the green trait of plant fruits. Figure 5(a) It can be seen that the 0 kGy group, which underwent pre-treatment with greening agents on day 0, significantly increased the chlorophyll content of broccoli. However, after subsequent electron beam irradiation treatment, the chlorophyll content showed a trend of first decreasing and then increasing with increasing irradiation intensity. Notably, the chlorophyll content of all broccoli groups decreased significantly with the extension of subsequent storage time, except for the 6 kGy group, which showed no significant difference in chlorophyll content on days 2 and 4 of storage. This indicates that electron beam irradiation at a dose of 6 kGy delayed the decomposition of chlorophyll in broccoli during storage, a result consistent with the trend of the color index a* value. These results suggest that pre-treatment with greening agents increased the chlorophyll content of broccoli, and subsequent electron beam irradiation more effectively delayed the decomposition of chlorophyll.

[0086] 3.2.2 Effects of electron beam irradiation on the antioxidant capacity of broccoli

[0087] MDA (malondialdehyde) content is related to the degree of membrane lipid peroxidation. During normal storage of plant fruits, the plant respiration rate increases, leading to a gradual increase in organic matter consumption and thus MDA accumulation. As shown in Table 1, MDA gradually accumulates with prolonged storage time. However, compared with the control group (CK), the 0 kGy group showed a reduction in broccoli MDA content. Subsequent electron beam irradiation significantly reduced broccoli MDA content. On day 0, the MDA content of the CK group was 2.30 times and 2.09 times that of the 6 kGy and 8 kGy groups, respectively, with the largest reduction observed at the 6 kGy dose. This indicates that electron beam irradiation has a positive effect on extending the shelf life of broccoli. MDA content is closely related to vegetable senescence; an increase in MDA content indicates a decline in broccoli quality. Pre-treatment with greening agents also reduced broccoli MDA content during storage. Subsequent irradiation treatment, in synergy, significantly inhibited the growth rate of MDA during storage, greatly slowed down membrane lipid peroxidation, reduced MDA content, and maintained broccoli quality. Irradiation treatment may have repaired the damage to the broccoli's cell membrane, maintaining the integrity of the cell membrane and thus resulting in a lower MDA content than the CK group.

[0088] Table 1. Effects of electron beam irradiation on MDA content in broccoli.

[0089]

[0090] Figure 5 (b) and Figure 5 (c) The effects of different doses of electron beam irradiation on the total phenolic content and DPPH free radical scavenging rate of broccoli are shown. Figure 5 (b) and Figure 5(c) It can be seen that on day 0 after electron beam irradiation treatment, the total phenol content and DPPH radical scavenging rate at doses of 4 kGy, 6 kGy, and 8 kGy were significantly higher than those in the control group (CK), with the total phenol content in the 6 kGy irradiation group being 1.65 times higher than that in the CK group. The DPPH radical scavenging rate of the broccoli in the 6 kGy group showed the greatest difference on day 2, with the DPPH radical scavenging rate at the 6 kGy dose being 1.6 times higher than that in the CK group. However, during the subsequent storage period of 4-6 days, the differences between the groups gradually narrowed, reaching the highest DPPH radical scavenging rate in the CK group on day 6, with all irradiated groups showing significantly lower rates than the CK group. Notably, the DPPH radical scavenging rate under the 8 kGy dose irradiation treatment was consistently lower than that in the CK group, a trend also reflected in the changes in total phenol content. It is speculated that this may be because excessively high doses of electron beam irradiation damage the microstructure of the samples, and its destructive effect is stronger than that of low-dose treatment, leading to damage to antioxidants or structures. Experimental results show that electron beam irradiation can simultaneously enhance the antioxidant capacity and total phenolic content of broccoli in the early stages of storage. Electron beam irradiation may improve antioxidant capacity by promoting an increase in polyphenol content. The increased DPPH scavenging rate of broccoli after electron beam irradiation is due to the increase in polyphenolic compounds. Phenolic compounds have strong antioxidant properties, and the antioxidant activity increases with the increase in total phenolic content. Electron beam irradiation can increase cell permeability and improve the cell's metabolic rate, which may be the reason for the accumulation of phenolic substances in irradiated broccoli.

[0091] 3.3 Total bacterial count

[0092] Microorganisms are a crucial factor affecting the shelf life of vegetables and are essential for ensuring their quality during sale. Ionizing radiation can directly inhibit microbial growth and reproduction in broccoli through damage to the cell nucleus or the indirect action of free radicals formed by water lysis within cells. It can also penetrate deep into the tissues of the fruit, killing putrefactive microorganisms on the tissues and surface, thus achieving sterilization and delaying spoilage and aging. Table 2 shows that as storage time increased, the total bacterial count in the control group (CK) reached an uncountable number by the second day. For the broccoli treated with the "Green Protection Plus Irradiation" group, no bacterial colonies were detected in the broccoli treated with 4 kGy, 6 kGy, and 8 kGy doses during the 0-6 day storage period. While the 2 kGy group did not achieve sterility, the total bacterial count in the 0-4 day period was significantly lower than that in the CK and 0 kGy groups. This indicates that electron beam irradiation can effectively inhibit the growth and reproduction of microorganisms in broccoli, and that higher doses of electron beam irradiation have a better sterilization effect.

[0093] Table 2. Effects of electron beam irradiation on total bacterial count in broccoli.

[0094]

[0095] 3.4 Analysis of Volatile Compounds in Broccoli

[0096] To more intuitively compare the volatile flavor compounds of broccoli under different irradiation intensities and storage times, a heatmap visualization hierarchical cluster analysis was performed on the volatile flavor compounds detected by GC-MS. The results are shown in [Figure number missing]. Figure 6-8 In the heatmap, the relative content of each volatile substance is represented by different colors; the redder the color, the higher the relative content, and the bluer the color, the lower the relative content.

[0097] A total of 63 flavor compounds were detected in broccoli by GC-MS, mainly including alcohols (10), aldehydes (4), ketones (5), acids (4), esters (3), hydrocarbons (19), sulfur-containing compounds (7), and other compounds (11). 25 compounds with a VIP>1 were screened out through analysis (Table 3).

[0098] Studies have shown that alcohols and sulfides are the main sources of variation in volatile compounds during broccoli storage. Dimethyl disulfide, dimethyl trisulfide, and other sulfides, as well as 1-hexanol, 1-pentanol, and nonanal, are the main contributors to off-odors in broccoli during storage. Volatile sulfur compounds in broccoli, such as dimethyl disulfide and dimethyl trisulfide, produce an unpleasant sulfurous odor, similar to cabbage, severely affecting the quality of broccoli. Experimental results showed that the concentration of dimethyl disulfide in the 6 kGy electron beam irradiation treatment on day 0 was 2.24 times lower than that in the 0 kGy group. Acetic acid has a pungent sour taste and is closely related to the degree of contamination and quality deterioration in broccoli. Broccoli deteriorates during storage, releasing compounds such as acetic acid and nonanol. On day 6 of storage, the acetic acid concentration in the 6 kGy group was 5.16 times and 4.47 times lower than that in the control group and the 0 kGy group, respectively. These results indicate that irradiated broccoli shows quality deterioration after 2 days of storage at room temperature, affecting its edibility. After treatment with 6 kGy electron irradiation, the concentrations of acetic acid and nonanoic acid decreased significantly. Figure 8It can be seen that the number of flavor compounds in broccoli showed a trend of first increasing and then decreasing. At 2, 4, and 6 days of storage, the number of flavor compounds in the 6 kGy group (35, 27, 26) was lower than that in the CK group (42, 44, 43) and the 0 kGy group (43, 32, 31), indicating that electron beam irradiation treatment reduced the number of flavor compounds in broccoli. In addition, an isothiocyanate, a common bioactive substance in cruciferous plants with anti-cancer and antioxidant effects, was also detected in the flavor compound analysis. After 6 kGy irradiation treatment, the concentration of erucin increased from 0.60 μg / kg to 3.33 μg / kg. These results indicate that electron beam irradiation has a significant impact on the content of volatile compounds in broccoli, can alter the aroma characteristics of broccoli during storage, and may enhance the nutritional potential of broccoli.

[0099] Table 3. Volatile flavor compounds in broccoli from different treatment groups

[0100]

[0101] In summary, this experiment investigated the synergistic effects of electron beam irradiation (0, 2, 4, 6, 8 kGy) and pretreatment on broccoli quality during a 6-day storage period. Specifically, it studied the effects of pretreatment combined with electron beam irradiation of different intensities on broccoli firmness, color, MDA content, total phenolic content, DPPH free radical scavenging rate, chlorophyll content, microbial colony count, volatile compounds, and sensory evaluation. The aim was to evaluate the effectiveness and applicability of pretreatment combined with electron beam irradiation for preserving plant fruits, particularly its impact on the overall quality of broccoli during storage and the feasibility of the preservation method. This study shows that the greening pretreatment combined with electron beam irradiation effectively delayed broccoli senescence and inhibited changes in color and deterioration of sensory quality. Specifically, it suppressed the rate of decrease in a* value and the rate of MDA growth, increased total phenolic content and antioxidant capacity, and maintained good color and chlorophyll content. High-intensity electron beam irradiation treatment showed better results, reducing the number of microorganisms. Broccoli irradiated at doses of 4 kGy, 6 kGy, and 8 kGy achieved a sterile state. Among these, the combined application of 6 kGy electron beam irradiation and pretreatment yielded the best overall effect, more effectively preventing losses caused by quality degradation and decreased consumer acceptance during storage. Furthermore, the types and concentrations of volatile flavor compounds changed significantly after pretreatment combined with electron beam irradiation. In conclusion, the results indicate that the synergistic effect of pretreatment combined with electron beam irradiation can effectively delay the quality deterioration of broccoli, extend its shelf life, and reduce off-odors during the deterioration process. To a certain extent, it can extend the shelf life of broccoli stored at room temperature. Further combined applications such as controlled atmosphere storage or refrigeration hold promise for improving the preservation of post-harvest vegetables and fruits.

[0102] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of the claims of this patent application.

Claims

1. A method for extending the shelf life of broccoli based on electron beam irradiation technology, characterized in that: The method comprises the following steps: Step one, preparing a green-protecting solution and adjusting the pH of the solution to 6.0-6.5 for standby; Step two, immersing the selected broccoli in the green-protecting solution and then performing microwave treatment; Step three, performing high-temperature enzyme inactivation treatment on the microwave-treated broccoli and then immediately placing the broccoli in ice water to rapidly cool to room temperature; Step four, sealing the treated broccoli in a vacuum packaging bag and then performing electron beam irradiation treatment.

2. The method for extending shelf life of broccoli based on electron beam irradiation technology according to claim 1, characterized in that, In step one, the green-protecting solution comprises the following components at the following concentrations: 0.25-0.35 g / L of sodium copper chlorophyllin, 0.90-1.05 g / L of ascorbic acid, and 1.70-1.80 g / L of tea polyphenol.

3. The method for extending shelf life of broccoli based on electron beam irradiation technology according to claim 1, characterized in that, In step one, the pH of the solution is adjusted to 6.5 by adding an adjusting agent.

4. The method for extending shelf life of broccoli based on electron beam irradiation technology according to claim 3, characterized in that, The adjusting agent is a lye.

5. The method for extending shelf life of broccoli based on electron beam irradiation technology according to claim 1, characterized in that, In step two, the ratio of broccoli to the green-protecting solution is 1:3-1:5 g / mL.

6. The method for extending shelf life of broccoli based on electron beam irradiation technology according to claim 1, characterized in that, In step two, the specific method of microwave treatment is as follows: after the broccoli immersed in the green-protecting solution is treated in a microwave device with a power of 550-650 W for 0.5-1 min, the broccoli is left to stand for 15-25 min.

7. The method for extending shelf life of broccoli based on electron beam irradiation technology according to claim 1, characterized in that, In step two, before the selected broccoli is immersed in the green-protecting solution, the broccoli is pretreated by being sequentially cleaned with a sodium hypochlorite solution and distilled water.

8. The method for extending shelf life of broccoli based on electron beam irradiation technology according to claim 1, characterized in that, In step three, blanching is used for enzyme inactivation treatment, wherein the blanching temperature is 95-105 ℃ and the blanching time is 25-35 s.

9. The method for extending shelf life of broccoli based on electron beam irradiation technology according to claim 1, characterized in that, In step four, the radiation dose of electron beam irradiation is 0-8 kGy.

10. The method for extending shelf life of broccoli based on electron beam irradiation technology according to claim 9, characterized in that, The radiation dose of electron beam irradiation is 6 kGy.

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